During their operation, electronic devices such as microprocessors, other integrated circuits, and other electronic components produce heat. Sometimes, the amount of heat produced and/or the attributes of the electronic device are such that this heat must be removed from the device. Failure to remove the heat from such devices can cause its operating characteristics to deteriorate. Deterioration of these operating characteristics can cause problems for the systems that incorporate these electronic devices. In some cases, failure to adequately remove the heat can lead to the failure of the device. Such problems can be troublesome and costly.
To prevent such problems from occurring, cooling can be provided to electronic components. One means of cooling electronic components is the heat sink. Heat sinks have long been used to remove heat from electronic devices to which the heat sinks are attached. Heat sinks can comprise a mass of thermally conductive material such as a metal like copper or aluminum. Heat sinks can be attached to the top or another surface of the electronic device to be cooled. Heat produced within the electronic device is transferred by conduction into the heat sink mass. The heat is then transferred away from the heat sink primarily via convection. Some of the heat can also be removed via radiation.
To promote convective heat transfer from them, some heat sinks are designed to include a plurality of fins on their upper surface. The heat is conducted through the heat sink and into the fins. There, the heat radiates off and away from the heat sink. The fins also radiate heat. Fins can comprise an array of plano-linear appendages running parallel to one another across the surface of the heat sink and parallel to the flow of air across them, as shown in Prior Art FIG. 1. Fins can also comprise an array of pins, posts, or similarly configured appendages raised from the surface of the heat sink. Heat transfer from the heat sink via the fins is proportional to the surface area of the fins.
Air (or another gas) filling the interior of the housing of a component or system of which the electronic device being cooled is a part provides a medium for convective heat transfer away from the fins, and thus serves to promote cooling of the device. Convection typically provides a significant portion of the device's cooling. Convective heat transfer is proportional to the mass flow rate of a cooling medium across the heated surface. Thus, convective cooling can be made more effective by providing or increasing the flow of the fluid across the fins. The flow rate can be increased by the use of mechanical ventilating components such as fans.
Some electronic devices are provided with their own dedicated cooling fans, such as those mounted integrally with its heat sink pin fin structure. Electronic systems such as computers and servers, which can incorporate a multitude of heat producing electronic components, sometimes provide cooling media in the form of fan-blown air. The air blowing through the internals of the system removes the heat produced by the components therein. As the air warmed by this heat leaves the system, it carries the heat with it into the room or other milieu in which the system operates. Sometimes this heat is further dissipated, such as by external fans, or removed, such as by air conditioning and ventilation.
For some electronic systems such as enterprise servers and other business-critical systems, operational reliability is an significant if not crucial attribute. Where operational reliability is necessary, cooling of component devices is such an important function that multiple fans are used therein for redundancy. As shown in Prior Art FIG. 1, redundant fans 11 and 12 are conventionally mounted coaxially so that during normal operations, the first fan 11 discharges its air into the suction of the second fan 12. This arrangement provides more than adequate air flow 16 from one direction across heat sink 13, parallel to its fin appurtenances 15, so as to cool electronic device 14 by forced convection.
The output volume, pressure, and mass flow rate of the discharge of a single fan, either 11 or 12, is designed to suffice to adequately cool device 14. Thus fans 11 and 12 are redundant; if fan 11 fails, fan 12 should suffice and vice versa. However, a frequent failure mode for fans used in cooling electronic equipment is bearing failure. Typically, such bearing failures occur when a bearing seizes, which can stop (or initially slow and progress to stop) the rotation of the fan. Blades 20 of fans 11 and 12 do not feather, but retain their pitch. Thus if either fan stops by bearing seizure, blades 20 of the stopped fan are static in the airstream and can aerodynamically impede the air flow from the redundant fan.
In such a case, the redundant fan can provide less than its design air discharge, such that air flow 15 can be reduced to less than half of the design discharge of both operating fans. When air flow 15 is thus reduced, it may not provide adequate cooling for electronic device 14, and the purpose of having the redundant fans can be impeded or defeated.
Other heat sink designs such as pin finned heat sinks allow cooling from any direction or from multiple directions. However, pin fin and other such heat sinks are less efficient than plano-linearly finned heat sinks in both heat transfer and pressure drop. Other methods of cooling electronic devices besides heat sinks have been implemented to avoid these shortcomings. These solutions include heat pipes and vapor chambers. However, both heat pipes and vapor chambers are typically expensive with respect to heat sinks, and have their own reliability issues, such as leakage failure.
Further, fans (including redundant pairs) are sometimes used with the heat pipes and vapor chambers to remove the heat therefrom, such that cooling reliability can remain a concern even when these alternatives are used. Adding additional fans to systems whose components are cooled by either heat sinks or alternatives can be expensive and pose spatial and physical arrangement challenges within the systems. This can be exacerbated by the placement of components such as power supplies and circuit boards. These can restrict or block air flow add more heat. Hence, conventional solutions to removing heat from electronic devices may not be entirely adequate in some applications.